From d298b41f90cbf1f2e5a10e29daa1fc92ddee52c9 Mon Sep 17 00:00:00 2001
From: Javier Martinez Canillas <javierm@redhat.com>
Date: Wed, 14 Oct 2020 16:33:42 +0200
Subject: [PATCH] mmap: Don't register cutmem and badram commands when lockdown
 is enforced

The cutmem and badram commands can be used to remove EFI memory regions
and potentially disable the UEFI Secure Boot. Prevent the commands to be
registered if the GRUB is locked down.

Fixes: CVE-2020-27779

Reported-by: Teddy Reed <teddy.reed@gmail.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
---
 docs/grub.texi        |  4 ++++
 grub-core/mmap/mmap.c | 13 +++++++------
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/docs/grub.texi b/docs/grub.texi
index 98592d3..f2fe149 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4051,6 +4051,10 @@ this page is to be filtered.  This syntax makes it easy to represent patterns
 that are often result of memory damage, due to physical distribution of memory
 cells.
 
+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
+      This prevents removing EFI memory regions to potentially subvert the
+      security mechanisms provided by the UEFI secure boot.
+
 @node blocklist
 @subsection blocklist
 
diff --git a/grub-core/mmap/mmap.c b/grub-core/mmap/mmap.c
index 57b4e9a..7ebf32e 100644
--- a/grub-core/mmap/mmap.c
+++ b/grub-core/mmap/mmap.c
@@ -20,6 +20,7 @@
 #include <grub/memory.h>
 #include <grub/machine/memory.h>
 #include <grub/err.h>
+#include <grub/lockdown.h>
 #include <grub/misc.h>
 #include <grub/mm.h>
 #include <grub/command.h>
@@ -534,12 +535,12 @@ static grub_command_t cmd, cmd_cut;
 
 GRUB_MOD_INIT(mmap)
 {
-  cmd = grub_register_command ("badram", grub_cmd_badram,
-			       N_("ADDR1,MASK1[,ADDR2,MASK2[,...]]"),
-			       N_("Declare memory regions as faulty (badram)."));
-  cmd_cut = grub_register_command ("cutmem", grub_cmd_cutmem,
-				   N_("FROM[K|M|G] TO[K|M|G]"),
-				   N_("Remove any memory regions in specified range."));
+  cmd = grub_register_command_lockdown ("badram", grub_cmd_badram,
+                                        N_("ADDR1,MASK1[,ADDR2,MASK2[,...]]"),
+                                        N_("Declare memory regions as faulty (badram)."));
+  cmd_cut = grub_register_command_lockdown ("cutmem", grub_cmd_cutmem,
+                                            N_("FROM[K|M|G] TO[K|M|G]"),
+                                            N_("Remove any memory regions in specified range."));
 
 }
 
-- 
2.14.2

